Probably not. Scaling up a gun is more difficult than to scale one down. The 7.62 NATO is quite a bit more powerful than the 5.56 NATO. It will involve a lot of work to make the FA MAS fire the 7.62mm round.

In the good old days of the Cold War, I recall there was lots of talk of producing a single calibre bullet/weapon, for NATO forces and our American allies, but obviously it did`nt gt off the ground, probably as a result of no one agreeing on which one would be adapted or approved, SLR 7.62 was considered too powerful, and 5.56 was the alternate option, but some considered that to be underpowered, seems to me we should have gone for the Kalashnikov, surely in a battle if you lost yours there would be loads of them lying around, and knowing the rough treatment they can take, at least there was a good chance of it working